1. Field of the Invention
The present invention relates to a compact projection system increasing optical efficiency by using a hologram and a scrolling unit.
2. Description of the Related Art
As illustrated in FIG. 1, a conventional projection system includes a light source 100, first and second relay lenses 102 and 110, a color wheel 105, a fly-eye lens 107, a light valve 112, and a projection lens unit 115. The first relay lens 102 focuses a beam emitted from the light source 100 onto the color wheel 105, which separates the incident beam into three color beams of light, namely, R, G, and B beams. The fly-eye lens 107 makes the R, G, and B beams transmitted by the color wheel 105 uniform. The second relay lens 110 then focuses the R, G, and B beams transmitted by the fly-eye lens 107 onto the light valve 112, which forms a picture using the R, G, and B beams sequentially emitted from the color wheel 105. The projection lens unit 115 advances the formed picture toward a screen 118.
In the conventional projection system, color images are obtained by rotating the color wheel 105 at a high speed using a driving motor (not shown) and sequentially radiating R, G, and B beams to the light valve 112. The color wheel 105 is equally divided into three color filters, namely, R, G, and B filters. Accordingly, when the color wheel 105 rotates, in accordance with the response speed of the light valve 112, the three color filters are sequentially used to form the R, G, and B beams. This operation results in a light loss corresponding to ⅔ of an incident beam. Light loss is also generated by a predetermined gap formed between two adjacent color filters, typically to achieve better color images.
In addition, because the color wheel 105 rotates at a high speed, noise is also generated. Further, the mechanical rotation of the color wheel 105 causes the motion of the color wheel 105 to be unstable. The driving motor to rotate the color wheel 105 also contributes to an increasing of the size of the color wheel 105. Since the color wheel 105 cannot accelerate over a certain speed, due to a mechanical limit of the driving motor, color breakup also occurs. Furthermore, projection system manufacturing costs also increase because of the color wheel being very expensive.